The instructor sounds like a total jerk. I bet he's a young instructor with a chip on his shoulder about women.
I'm sorry but it is his responsibility to TEACH you and if he isn't teaching the students properly then he is at fault.
If a technique doesn't work for one of my students I try to find other ways until I find something that will help them learn to do it.
Just because he's there in front of the class does not mean he has the right to belittle and degrade the students performances. Teaching Martial arts is about helping each other to learn, and being respectful of peoples abilities, not showing off in front of the class and making students lives a misery.
Keep asking him to show you how to do it properly, and if he won't or can't help you then I'd leave and go to a dojo that will treat you with respect. You will go much further and enjoy it while you are doing it.
HE needs to learn how to be a better teacher IMHO. He wouldn't last 5 minutes in my dojo with an attitude like that!
You stand up tall and talk to him. Be brave, you can do it!
Tell him from me that all students need respect, if he doesn't get it then you know what to do.
In my experience some male instructors are not good at working with us women, so they try to make things hard so that the women leave so they don't have to cope with it, whereas they need to grow up themselves and get a life.